Aspects of the ecology and population genetics of the bivalve Corbula gibba

Abstract

The bivalve mollusc Corbula gibba (Olivi) is often regarded as an invasive weed species that forms monospecific stands in organically enriched hypoxic habitats. However, despite its status as a potential menace, surprisingly little is known about its basic biology, including its dispersal capacity. Measurement of the respiration rate of C. gibba revealed a respiratory demand of 3.12 μl O2 h-1 and a respiratory quotient of 0.61, which suggests that C. gibba adopts a conservationist rather than exploitative mode of life. Examination of the hypoxic tolerance of C. gibba determined that adults could survive for >34 d (LT50 ≥ 34 d) and juveniles for >30 d (LT50 = 14 d), indicating that this species is well adapted to living in low oxygen habitats. Unusually, adults under hypoxia had a greater survival rate than control adults in normoxic conditions. Investigation of the salinity tolerance of C. gibba revealed that it could readily survive for 2 d at 0 to 16 psu, with increasing mortality for up to 10 d. In brackish seawater, survival was indistinguishable from that in normal seawater. Examination of the population genetics of 6 different populations of C. gibba separated over various spatial scales, using RAPD PCR methodology, determined that all populations were genetically distinct from each other, including populations separated by as little 5 km, although this may in part be due to the influence of a localised front. This suggests that the larval longevity and dispersal capacity of C. gibba is much less than has been previously considered. In light of all the results, it is concluded that instead of being an insidious pest species, C. gibba is more likely to be an inferior competitor, present in background numbers in normoxic habitats, and only becomes dominant when a system becomes hypoxic, thereby removing competitors and allowing C. gibba to flourish in the habitat to which it is adapted. © Inter-Research 2006.